The use of imaging equipment has penetrated, over the years, into almost every field and has become an essential aid for accomplishing a variety of tasks. Imaging equipment is used in a wide range of security systems, to monitor sensitive locations and facilities, and to provide a reliable and cost-effective solution for perimeter security. An additional use for imaging equipment is in the military, where image-based systems are used for reconnaissance gathering, enhanced situational awareness, automatic navigation and for many additional human-operated as well as automated systems.
In the medical field imaging devices are also used; during endoscopic procedures, for example, a surgical scope is inserted into body cavities for imaging the inner body for diagnostic and surgical purposes.
Imaging devices are used in many additional fields, some commercial, and others for private, home use, for purposes of entertainment, photography and even baby monitoring.
Prior art techniques of imaging rely on the use of an image sensing device equipped with an optical lens. The prior art optical lenses are designed to cover a specific-sized field of view, and transmit this field of view to be captured by the image sensing device. While most optical lenses presented in the prior art provide the ability to capture a field of view limited in its aperture, a need exists to capture an unlimited field of view, or an omni-directional field of view, i.e. a panoramic (cylindrical) field of view or a nearly spherical field of view.
An optical lens that covers an omni-directional field of view and enables the image sensing device to capture that omni-directional scene simultaneously would provide significant improvement to imaging devices. The omni-directional scene that would be covered would enable constant awareness of the omni-directional scene. The advantages of such an optical lens are obvious—security systems will have no “dead zones” and will constantly cover and monitor the omni-directional scene. Medical scopes will provide the surgeon with the ability to view the entire environment in which he operates and avoid the risk of injuring inner body tissue or cause breach of blood vessels which were previously obscured from his view. Military systems will also benefit from the ability to view an omni-directional scene and so will most systems based on image sensing, whose performance is currently limited by the limited aperture provided by their optical lenses.
Some techniques of panoramic imaging have been presented in prior art, and those make use of several image capture devices, each one aimed at a different sector limited in width, combined in a manner that all of them together, when properly aligned, cover a full 360 degrees field of view. Another prior art method for panoramic imaging relies on a single image capture device, rotated around a vertical axis. In this method the image capturing device covers a limited sector at any single moment, but while completing a full rotation, it creates a sequence of images which are combined together to a panoramic image. In this method it is impossible to see simultaneously and in real-time the omni-directional scene.
The main disadvantage of the above mentioned prior art methods is their relative complexity. Some of the prior art methods necessitate moving/rotating mechanisms, require frequent alignment and very often turn out to be maintenance-intensive.
A different prior art approach makes use of axis-symmetric reflective surfaces, used to reflect an omni-directional field of view towards a single image-capture device. In this approach a circular image is formed on the focal plane array of the image capture device. The shape of the image derives from the reflection of the surrounding field of view by the reflective surface. The image shape and possible aberrations are corrected by image processing techniques. A sub-group of the said technique makes use of two reflective surfaces designed to doubly reflect the omni-directional field of view towards the image capture device. Such a design is described in U.S. Pat. No. 6,426,774. In the said patent, a convex axis-symmetric reflective surface reflects a cylindrical field of view towards a flat reflective surface located coaxially with it. A circular image is reflected from the convex axis-symmetric surface towards the flat reflective surface and then reflected towards an image capture device, which is located at the concave side of the convex reflective surface, through a hole located at the center of the axis-symmetric convex reflective surface.
Additional methods have been developed to achieve capture of an enlarged field of view of an almost spherical scene. Such a design is described in WO02/059676, the description of which, including reference cited therein, is incorporated herein by reference in its entirety. In the said publication, two reflective surfaces are used, in both of which a transparent area is formed at the center to enable penetration of beams originating at an additional scene, which is not covered by the reflective surfaces. As a result of the unique design, a nearly spherical field of view is captured, comprising a cylindrical field of view doubly reflected by the reflective surfaces towards the image capture device, and an additional field of view penetrating through the said transparent areas towards the image capture device. The said transparent areas may be fabricated either as transparent surfaces or as optical lenses which enhance the properties of the additional scene.
The mentioned prior art techniques represent methods of acquiring a large field of view, using optical structures which comprise several separate optical components.
In view of the deficiencies of the prior art, it would be desirable to provide an optical lens that enables coverage of a panoramic or nearly spherical field of view by utilizing a monolithic optical block, which incorporates all refractive and reflective surfaces needed to acquire the scene. As a result of the shape of such an optical block and its surfaces, aberrations would be reduced to an acceptable level and generally there would be need of additional correction lenses along the optical path, thus simplifying the optical design and structure and reducing production costs.
It is therefore an object of the present invention to provide such an optical lens designed to cover a panoramic field of view.
It is another object of the present invention to provide an optical lens designed to cover a nearly spherical field of view.
It is yet another object of the present invention to provide methods of illuminating the omni-directional scene that is to be imaged, using an optical lens as both the omni-directional illumination distributor and as the optical element designed to collect the image of the omni-directional scene.
Additional objects of the invention would become apparent as the description proceeds.